[ovs-dev] [PATCH v2 1/5] ofproto-dpif-xlate: Don't unwildcard tunnel attributes on set.

Daniele Di Proietto diproiettod at vmware.com
Tue Oct 4 00:42:19 UTC 2016


I'm rebasing the series and considering a different approach for this.

I'll send something shortly.

Thanks,

Daniele

On 03/10/2016 17:38, "Ben Pfaff" <blp at ovn.org> wrote:

>Does this patch need anything more?  I don't see it on master and it's
>still in patchwork.  Same thing for patch 4/5 in this series.
>
>On Thu, Sep 01, 2016 at 01:31:06AM +0000, Daniele Di Proietto wrote:
>> 
>> On 31/08/2016 11:32, "Jarno Rajahalme" <jarno at ovn.org> wrote:
>> 
>> >I’d put the registers and metadata field to the ‘false’ and also maybe non-writeable fields (ether type, frags, nw_proto, etc.) in to OVS_NOT_REACHED() case, just in case.
>> >
>> >  Jarno
>> 
>> Agreed, done
>> 
>> Thanks,
>> 
>> Daniele
>> 
>> >
>> >> On Aug 31, 2016, at 10:38 AM, Jesse Gross <jesse at kernel.org> wrote:
>> >> 
>> >> On Tue, Aug 30, 2016 at 6:47 PM, Daniele Di Proietto
>> >> <diproiettod at vmware.com> wrote:
>> >>> When translating a set action we also unwildcard the field in question.
>> >>> This is done to correctly translate set actions with the value identical
>> >>> to the ingress flow, like in the following example:
>> >>> 
>> >>> flow table:
>> >>> 
>> >>> tcp,actions=set_field:80->tcp_dst,output:5
>> >>> 
>> >>> ingress packet:
>> >>> 
>> >>> ...,tcp,tcp_dst=80
>> >>> 
>> >>> datapath flow
>> >>> 
>> >>> ...,tcp(dst=80) actions:5
>> >>> 
>> >>> The datapath flow must exact match the target field, because the actions
>> >>> do not include a set field. (Otherwise a packet coming in with a
>> >>> different tcp_dst would be matched, and its port wouldn't be altered).
>> >>> 
>> >>> Tunnel attributes behave differently: at the datapath layer, before
>> >>> action processing they're cleared (we do the same at the ofproto layer
>> >>> in xlate_actions()).  Therefore there's no need to unwildcard them,
>> >>> because a set action would always be detected (since we zero them at the
>> >>> beginning of xlate_ations()).
>> >>> 
>> >>> This fixes a problem related to the handling of Geneve options.
>> >>> Unwildcarding non existing Geneve options (as done by a
>> >>> set_field:X->tun_metadata<n> on a packet coming from a non-tunnel
>> >>> interface) would be problematic for the datapaths: the ODP translation
>> >>> functions cannot express a match on non existing Geneve options (unlike
>> >>> on other attributes), and the userspace datapath wouldn't be able to
>> >>> translate them to "userspace datapath format".  In both cases the
>> >>> installed flow would be deleted by revalidation at the first
>> >>> opportunity.
>> >>> 
>> >>> Signed-off-by: Daniele Di Proietto <diproiettod at vmware.com>
>> >> 
>> >> I think there might be some more obscure ways of triggering this
>> >> problem that still exist. Basically anything that can use a register
>> >> as a target is a potential issue. For example, stack_pop, bundle, and
>> >> multipath all look like they have the same masking behavior.
>> >> 
>> >> I do have a general solution in this patch (look at the bottom of
>> >> xlate_actions() where it is adjusting the wildcards):
>> >> http://openvswitch.org/pipermail/dev/2016-August/078484.html
>> >> 
>> >> I didn't realize that it was addressing an existing issue though and
>> >> that patch certainly isn't suitable for anything other than master.
>> >> 
>> >> I'm also not really a big fan of the way I handled it there since it's
>> >> a pretty coarse way to do it. I would be happy to drop it if we can
>> >> feel comfortable that we got all of the callsites (now and in the
>> >> future) using your method. Perhaps we can just create a helper
>> >> function with this check builtin and then use it everywhere? That
>> >> might be enough to be confident about the future.
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>> >
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